I have a 30 gallon tank with 4 silver dollars and 1 gauromme. The tank population has been stable for 18 months. Yesterday I noticed one of the silver dollars with 2 flesh-colored swellings on the right side. The larger one is about 3 mm at widest diameter. The skin is not broken, and the fish seems to swim well but is not eating as well as usual. I had the pet store test the water. They said the nitrates were 'borderline' and I need to change the water 20% for 3 days in a row. They suggested I isolate the silver dollar, so I have him in a one gallon tank now. He has not changed any in the last 24 hours. The others in the original tank still seem well. The person at the store suggested this is either some type of 'nodular disease' caused by parasites, for which there is no treatment. Does anyone have a suggestion as to what caused this or what to do next?